High-frequency electrical heating apparatus



March 10, 1953 yn-E 2,631,221

HIGH-FREQUENCY ELECTRICAL HEATING APPARATUS Filed March 26, 1951Patented Mar. 10, 1953 UNITED STATES .PATENr oF-Ficr. f

i i inron-Fimoiinnoi fi iii'rmou"HEa'rING I --John G. Littell, FlorhamPark, 'N. J., ass'ignor to Krem'entz &' Company, Newark, N. 'J .,acorporation of New Jersey Application-March 2e, l9 51,-.Serial No.'217,566

"This invention relatesto a circuit-for heatin small non-ferrous metaldevices such as 'are used in "the jewelry trade.

In general this present invention relates to an improvement over PatentNo. 2,493,269.. issued January 3, 1950, to Harrison 'D; Simpson.Thispatent sets forth in considerable detail'the use of highfrequency'apparatus for the purpose "just'described. The patent alsopoints out inconsiderable detail the prior art 'methods which had beenin use, or at-least'tried out'prior to the filing of the application forsaid patent. In'view'of these disclosures it does not seem. necessaryto-discuss the-'prior-art' set forth :in the patent, except tomentionthat the present application is directed to improvements upon theapparatus disclosed in the Simpson patent.

@In'the use "oftheSimpson-patent, there is a difference in potential ofas much as350'0 volts 7 "betweenthe primary and secondary windings of I"the grid'transformer. Because these are of'ne cessity in close physicalproximity to obtain close coupling, the high voltage often arcedacrossbetweenthese windings, causingdamage to the insulation f thetransformeriwhich put it out of use until repairs wouldloe made.,Apparently this was partly due to theout of "phaserelation-betweenthe-primary and secondary voltages assisted by transientpeaks causedby-opening and closing of theswitch' controlling the plate cur rentaseach-piece was inserted in the'work coil. Several methods ofconstructing the grid transformer of said'patent weretriedin ordertoincrease the period-of time during which the apparatus couldbe-maintained in operatin condition. but none ofthese methods wereioundto be per-" fectlyf satisfactory.

It is. therefore the principal object or myl'present invention toprovide a grid transformer connected in the circuit in such a way as toeliminate all the trouble experienced with the apparatus of said-patent.My new arrangement comprises an auto-transformer having the grid of thevacuum tubeoscillator-connected to one end offthe transformer windingwhile the other end is connected to the anode-of theoscillator tube,with a ground connection made at the adjustable contact which is anadjunct of an auto-transformer. This pro-- vides an arrangement in whichone portion of the transformer is connected to the anode of theoscillator tube while the other portion is connected to the grid of thetube, the relation between the two portions being adjustable by reasonof the movable contact which in effect separates the transformer intoprimary and secondary windings with the primary being connected to the 5Claims. (01.219-47) plate of' the tube and the secondary to the grid.

With this arrangement 'thevoltage ratio of the two'coils can'beadjustedto produce an optimum of grid feed voltage and hence maximumefiiciency.

Furthermore, because the auto-transformer. is

a" single layer coil the-differencein'potential between anytwoconductorsthat-'arein close'phys- "ical'proximityis reduced from'3500 volts toabout 350 volts and arcing is-effectively"eliminated.

I have found that highly satisfactory-results can be obtained by usingan auto-transformer the helical or single layer coil of which is made upof copper tubingand having an outside diameter of the turns of 6 /2"andawinding length of approximately 2 using approximately ten :or eleventurns. The movable contactshould be preferably arranged so that it mayhe readily moved to vary the relationship between-the .primary andthesecondary sections.

The circuit arrangement with which this grid transformer is used is ingeneral the same as'that shown in the Simpson atent, however, there havebeen introduced certain circuit changes as can readily be seen byreferring tothe single figure of the drawing. In th circuit showing my'improvement is a step-up transformer I having a primary P which mayhave an ammeter A in'its circuit. The secondary 's is connected to tworectifier tubes 2 aud t which as-shown are of the gas type. Filaments ofthe tubes 2 and 3 are connected to the secondaryfi of the transformer 14 having a .-.primary 5. connected to J the a same source of l supply asthe primary P of thetrans- .Iform'er .1. :The ccenterztap :offthewinding ifi' is joined by a conductor 1 througharadio frequency."ldhdkfi zcoilig to -kee oscillations from ithe'lhigh frequencyoscillating itubeT-,out of .thei'source Ofdire'ct current coming fromthe .tubesi'Z and 3.

The tube.'I.-has aaplate :or vanode:9,:a. grid 10 and filament H thelatterof which is supplied with current from a-transformer lz'having aprimary .l3.and secondary 114. Connected to the anode of 2,681,221 j j pThe primary portion of the auto-transformer AT is connected in parallelacross the condenser l6 and the heating coil I'l. One end of the primaryis connected to the tube T through the blocking condenser 15, while thesecondary of the transformer has its free end 20 connected through aparallel arrangement of a grid bias resistor 24 and by-pass condenser 25to a parasitic suppressor composed of resistance 22 and inductance 2|arranged in parallel relationship and connected to the grid in. Themovable contact l9 of the transformer along with one side of thecondenser l6 and one end of the heating coil I! are connected to theground. The center of the winding I4 of the filament transformer I2 isalso grounded thereby giving a feedback circuit to the filament of thetube T. With this arrangement the connections from the secondary of thetransformer to the grid are in substantially a series circuit made up ofthe parts as just described. I have found with this arrangement whichhas been used over quite a period of time that troubles I have referredto have been overcome and overall improvement in efliciency ofapproximately three per-cent to five per-cent have been obtained overthe prior arrangement. Furthermore, the cost of the grid transformer hasbeen materially reduced and much time is saved in the operation of thesystem for the reasons heretofore explained.

I claim:

1. Means for heating metal parts including a high frequency oscillatorvacuum tube with means for feeding direct current to the plate of thetube, a tank condenser connected in the output circuit of the tube, aheating coil connected in parallel with the tank condenserand composedof few turns to facilitate the handling operation of the parts to beinserted into the space within said turns for heating them, an helicalsingle layer coil having few turns of large diameter with a movable tapconnected to that side of the tank condenser opposite to the side thatis connected to said tube plate and also one end of the auto transformerbeing operatively connected to said output circuit of the tube alongwith the condenser while the opposite end of the transformer isoperatively connected to the grid of the tube, and a blocking condenserconnected between the output of said tube and said tank condenser.

.2. Means for heating metal parts as set forth in claim 1 furtherdefined in that the connections to the grid of the tube includes aparasitic suppressor withv at least a condenser in series with. thesuppressor.

3. Means for heating metal .parts, including a high frequency triodetube and means for heatingits filament, means for supplying high voltagedirect current to the plate of said tube through denser being connectedbetween the plate of the triode tube and ground through the blockingcondenser, an helical single layer coil having few turns of largediameter having an adjustable contact and one portion between saidadjustable contact and one end, connected in parallel with the tankcondenser and heating coi1-while the other portion is operativelyconnected to the grid of said tube to provide a feedback voltagetherefor.

4. Means for heating metal parts as set forth in claim 3 further definedin that said feedback voltage to the grid is supplied through a gridbias resistor from the filament and a grid condenser connected to thelast mentioned portion of the auto transformer.

5. Means for heating metal parts including a high frequency oscillatortube with means for feeding current to the plate of the tube, a tankcondenser connected in the output circuit of the tube, a heating coilconnected in parallel with the tank condenser and composed of a fewturns to facilitate the handling operation of the parts to be insertedinto the space within said turns for heating them, an helical singlelayer coil having few turns of relatively large diameter and anadjustable tap, said coil having its primary end connected in parallelwith the tank condenser and the heating coil and the free end of thesecondary operatively connected to the grid of the tube to cause thesame to deliver a high frequency current to the heating coil that willproduce high heating in a matter of a very few seconds, and a blockingcondenser to keep high voltage direct current away from the resonantcircuit.

6. Means for heating metal parts including a grid-controlled vacuum tubewith means for feeding plate current and filament current to said tube,connected as a high frequency oscillator with a tank circuit in theoutput circuit of said tube comprising a condenser in parallel with aheating coil composed of few turns to facilitate handling of the workwithin said coil for heating the work, means for producing oscillationin said circuit including an helical single layer coil in parallel withsaid tank circuit with one endof said helical coil connected to saidtank condenser and a movable tap connected to said filament and with theother end of said coil connected through a bias resistor and gridcondenser to the grid, and a blocking condenser between the output ofthe tube and said tank condenser.

JOHN G. LITTELL.

REFERENCES CITED The following references are of record in the file ofthis patent:

Foley et al. Feb. 6, 1951

